Skeleton fitting techniques are used to adjust the parameters of a skeleton model to achieve a subject-specific result. One potential use for a subject-specific skeleton is the simulation of the subject's motion and subsequent analysis of the motion and its derived data, such as joint torques, muscle forces, or muscle energetics. A subject-specific skeleton should be tailored to the subject's physical and geometric parameters to produce an accurate and precise simulation. Conventional techniques of producing subject-specific skeletons suffer from a number of limitations.
In one conventional skeleton fitting process, a generic skeleton is manually and uniformly manipulated. This technique can produce an inaccurate result because human beings are not proportional. For example, applying a global scaling factor to a generic skeleton can generate incorrect individual segment sizes. In contrast to global scaling, some conventional techniques scale segments individually. These techniques can use motion-captured marker data to perform a one-dimensional (lengthwise) bone fitting. However, a subject-specific representation using a one-dimensional approximation typically does not match the subject's anthropometric body parameters because three-dimensional information is lost.
Another limitation of conventional skeleton fitting techniques is the inflexibility of the generic skeleton. In the implementation of conventional skeleton fitting techniques, a particular generic skeleton can become tightly integrated with the fitting process. Accordingly, improvements or changes to the generic skeleton can be difficult to integrate into the conventional fitting technique. The particular generic skeleton may also have limited joint types, for example, revolute joints with 3 degrees of freedom, which further limits the accuracy of the subject-specific model.
Although some optimization techniques exist for performing skeleton fitting from motion-captured marker data, these conventional techniques have several drawbacks. For example, one such conventional optimization technique is limited to estimating joint transformations (e.g., joint angles). Another conventional technique is limited because individual characteristics of bones are not accounted for.
What is needed is an apparatus and method that: (1) automatically constructs and scales a skeleton from motion-captured marker data; (2) applies to wide array of joint types; (3) optimizes joint transformations and bone geometric scale parameters in 3-dimensions using individualized factors; and (4) modularizes the integration of the generic skeleton.